The present invention relates to lighting control circuitry and more particularly to a novel control circuit for providing power and control voltages to an electronic ballast/lamp combination from a standard three-way socket to control the lamp light output level.
In this age of energy conservation, it is particular desirable to provide light sources producing luminous output equivalent to that of a standard incandescent bulb, at a reduced input from the electrical power mains. It is known that electronically-ballasted discharge lamps can be utilized to replace the relatively inefficient incandescent lamp. Of particular advantage is the "dimmable", or variable output, electronic ballast/discharge lamp combination described and claimed in co-pending U.S. patent applications Ser. No. 177,835, abandoned and Ser. No. 177,942, U.S. Pat. No. 4,346,332 both of which applications were filed Aug. 14, 1980, assigned to the assignee of the present application and incorporated herein in their entirety by reference. Briefly, the luminous output level of this ballast/lamp combination is variably responsive to the magnitude of an impedance between, or of a current shunted from, a pair of input control terminals. Additional input circuitry may be utilized to provide the shunting current, as well as a ballast/lamp on/off signal, responsive to the magnitude of a single D.C. control voltage, as described and claimed in co-pending U.S. patent application Ser. No. 242,782 filed on even date herewith, now U.S. Pat. No. 4,345,200, issued Aug. 17, 1982, assigned to the assignee of the present invention and also incorporated herein in its entirety by reference.
It is desirable to provide energy-efficient circuitry for allowing such an input-control/ballast/lamp combination to replace a standard "three-way" incandescent bulb, whereby the energy-efficient ballast/lamp combination can be mounted in a standard three-way socket, which previously accepted a three-way incandescent lamp, and which ballast/lamp combination is itself controlled by application of A.C. power to either, or both, of the "ring" and "button" contacts of the standard three-way socket to provide a selected one (e.g. off, dim, medium and high) of a plurality of lighting levels.
It is known to provide dimmer controls directly connected to the ballast, whereby replacement of an incandescent bulb with such a ballast/lamp combination requires that both the existing three-way switch and the ballast dimmer control be operated to vary the light output level; the socket switch merely provides an on/off switching action (such as by connecting the A.C. input contact of the ballast only to a single one of the ring and button contacts) while control of the actual light level, once the lamp has been switched to the on condition, is by action of the separate level control on the ballast package. This arrangement is extremely inconvenient for the consumer and is also relatively costly and of relatively low reliability. Accordingly, a control circuit which may be utilized between the standard three-way socket and the input of a control/ballast/lamp combination, to provide a plurality of lamp luminous output levels selected solely by the action of the three-way socket switch, is highly desirable.